In the past year, we have made a major breakthrough in the development of RNA-based tools for the in vivo imaging of cellular RNAs using fluorescence microscopy. Our collaborators in the Jaffrey laboratory at Cornell had previously reported the development of a fluorescent RNA module called 'Spinach' but further improvement was hampered by a complete lack of knowledge of its structural and biophysical basis of function. We have now determined the structure of Spinach, revealing a completely novel mode of RNA-fluorophore interaction, and have already employed the structure to both, design a minimized variant ('Baby Spinach') and to tune fluoresce properties.